What is the difference between Set Render Border and Set Render Border Camera Only?
SHIFT + B lets you select a portion that you wish to see in the final render image or in the camera view.



CTRL + B lets you select  a portion you wish to see in the render view mode. to then delete the border is CTLR + ALT + B



while CTLR + B works also in camera mode, SHIFT + B if is not in the camera view mode acts as a zoom tool.



CTLR + B does not affect the camera view or the final render. unless you are already in camera view